1. Field of the Invention
The present invention relates to a thin-film magnetic head having a magnetic pole that is formed of a plating film, and a method of manufacturing the same.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and magnetic recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has a structure in which a reproducing head including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a recording head including an induction-type electromagnetic transducer for writing are stacked on a substrate. The recording systems of magnetic recording devices include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. As compared with the longitudinal magnetic recording system, the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density.
Typically, the longitudinal magnetic recording system and the perpendicular magnetic recording system both use a thin-film magnetic head that has a structure in which a reproducing head including a magnetoresistive element (hereinafter, also referred to as an MR element) for reading and a recording head including an induction-type electromagnetic transducer for writing are stacked on a substrate. The recording head includes a magnetic pole that is made of a magnetic material. The magnetic pole includes a narrow portion and a wide portion, for example. The narrow portion has a front end face located in a medium facing surface that faces the recording medium, and a rear end opposite to the front end face. The wide portion is connected to the rear end of the narrow portion and has a width greater than that of the narrow portion. The magnetic pole produces, from the front end face of the narrow portion, a recording magnetic field for recording data on the recording medium. The width of the front end face of the narrow portion defines the track width. To increase the recording density, reduction in track width and improvement in recording characteristics, such as overwrite property which is a parameter indicating an overwriting capability, are required of the recording head.
A known method for forming the magnetic pole is to form the magnetic pole by plating in a groove that has a shape corresponding to the shape of the magnetic pole. For example, U.S. Patent Application Publication No. 2009/0162699 A1 describes a method in which a seed layer is initially formed in a groove of a pole-layer-encasing layer that is made of a nonmagnetic material, and then the magnetic pole is formed in the groove by plating. U.S. Patent Application Publication No. 2008/0316642 A1 describes a method in which a resist pattern that has an opening having a shape corresponding to that of the magnetic pole is formed on a nonmagnetic film. The nonmagnetic film and the resist pattern are used to form a groove, and an electrode film is formed in this groove before the magnetic pole is formed in the groove by plating.
A description will now be given of problems that occur with the formation of the magnetic pole having the narrow portion and the wide portion by using the method of forming the magnetic pole in a groove by plating. In such a case, the groove has a narrow groove portion for accommodating the narrow portion of the magnetic pole and a wide groove portion for accommodating the wide portion of the magnetic pole. An electrode film for plating is formed in the groove. In the process of forming the magnetic pole in the groove by plating, a plating film grows from the surface of the electrode film. Here, in the narrow groove portion, two portions of the plating film that are grown from two portions of the electrode film lying on two sidewalls of the narrow groove portion meet each other to form a seam between the two portions of the plating film. This results in a seam in the middle of the narrow portion as seen in the width direction.
The seam is a large, uniform crystal grain boundary. Impurities are apt to segregate on the seam. The seam therefore becomes low in mechanical strength and susceptible to corrosion as compared with the other areas of the magnetic pole. Consequently, if a seam is formed in the narrow portion of the magnetic pole, the magnetic pole becomes prone to defects in the process of manufacturing the thin-film magnetic head, such as a deep recess in the position of the seam. The magnetic material has a lower density at the seam than in the other areas of the magnetic pole. The presence of the seam in the narrow portion of the magnetic pole thus degrades the recording characteristics such as overwrite property.